Pavement markings convey information to drivers and pedestrians by providing exposed visible, reflective and/or tactile surfaces that serve as indicia upon a traffic surface. In the past such a function was typically accomplished by painting a traffic surface. Modern pavement marking materials offer significant advantages over paint such as dramatically increased visibility and/or retroreflectance, improved durability, and temporary removable marking options. Examples of modern pavement marking materials are thermoplastic, pavement marking sheet materials, tapes and raised pavement markers.
The Americans with Disabilities Act of 1990, published requirements for sidewalk and other potentially dangerous areas in that detectable warning devices would be required to warn blind or visually impaired and wheelchair bound individuals of potentially dangerous and vehicular traffic areas. Of particular note is section 4.29, §§0.2 as restated below:
4.29 Detectable Warnings
                4.29.2 Detectable Warnings on Walking Surfaces. Detectable warnings shall consist of raised truncated domes with a diameter of nominal 0.9 in (23 mm), a height of nominal 0.2 in (5 mm) and a center-to-center spacing of nominal 2.35 in (60 mm) and shall contrast visually with adjoining surfaces, either light-on-dark, or dark-on-light. The material used to provide contrast shall be an integral part of the walking surface. Detectable warnings used on interior surfaces shall differ from adjoining walking surfaces in resiliency or sound-on-cane contact.        4.29.3 Detectable Warnings on Doors To Hazardous Areas.        4.29.4 Detectable Warnings at Stairs.        4.29.5 Detectable Warnings at Hazardous Vehicular Areas. If a walk crosses or adjoins a vehicular way, and the walking surfaces are not separated by curbs, railings, or other elements between the pedestrian areas and vehicular areas, the boundary between the areas shall be defined by a continuous detectable warning which is 36 in (915 mm) wide, complying with 4.29.2.        4.29.6 Detectable Warnings at Reflecting Pools. The edges of reflecting pools shall be protected by railings, walls, curbs, or detectable warnings complying with 4.29.2.        
Detectable warning devices may be constructed as a preformed thermoplastic, thermoplastic, rubber, adhesive tile, tile cast into concrete, metal or other suitable material that will withstand abrasion and environmental extremes.
Formulations for preformed thermoplastic detectable warning devices, pavement markings and traffic control devices (preformed thermoplastic signage) are generically comprised of a:                Binder (˜20%) containing:                    Resin                            Maelic modified resin ester                C5 hydrocarbon, (for hydrocarbon class)                Rosin ester (for alkyd class)                Plasticizer                Vegetable oils                Phthalate esters                Mineral oil                Castor oil                Wax/Flexibilizer                Paraffin wax                Polyamide                EVA or SBS elastomers                                                Pigment (2-10%)                    Titanium dioxide            Lead chromate            Organic dyes            Filler (30-40%)            Calcium carbonate            Glass beads (30-40%)wherein the thermoplastic signage may be alkyd or hydrocarbon based. Thermoplastic signage must meet the standard specifications as published in the AASHTO—American Association of State Highway Transportation Officials). Designation: M 249-98                        
Continuous and skip lane stripings on highways and pedestrian crosswalk markings employ preformed pavement marking sheeting preferably comprising a wear-resistant top layer optionally overlying a flexible base sheet. The top layer is generally highly visible, may include retroreflective elements to enhance detection when illuminated by traffic at night, and serves as indicia when installed upon the roadway surface. Application of temporary pavement marking sheeting to a traffic surface has typically been by contact cement or rubber-based pressure-sensitive adhesives. Traffic surfaces may include surfaces for pedestrians motorized vehicles, aircraft, human powered conveyances, programmable robotics and the like.
Another example of a pavement marking is a raised pavement marker (i.e. a discreet marking structure with a rigid, semi-rigid or flexible marking body) which when applied to a roadway surface provides a raised surface. Often, the raised surface is both reflective and strategically oriented to enhance reflective efficiency when illuminated by traffic at night. In the case of rigid discreet markers, attachment of the body of each marker to the pavement surface has involved hot-melt adhesives or epoxy systems. Flexible body raised pavement markers have also been attached to pavement surfaces or pavement marking sheeting by soft butyl mastic materials.
In order to fulfill their function as indicia, raised thermoplastic detectable warning devices, pavement markers and pavement marking sheeting must be applied to a rather troublesome substrate. That substrate, the traffic surface, varies widely in terms of surface properties because the underlying material may be concrete or asphalt, may be of varying age and temperature, and may, on occasion, be moist or damp or oily. In this specific case, the pavement may still be uncured. Additionally, the roadway surface may vary in texture from rough to smooth. The substrate surface properties, therefore, represent a considerable challenge for attachment.
Specifically the standard for thermoplastic marking bond strength can be found in ASTM D4796-(2004), which states the test method and bonding strength of thermoplastic signage to concrete as: Bond Strength—After heating the thermoplastic material for four hours at 425 degrees F. the bond strength to Portland Cement Concrete shall exceed 1.24 MPa (˜180 psi). Preferably the bond strength is from about 200 psi to about 500 psi.
Thermoplastic signage therefore must reach a softening point within a range of about 400 degrees F. to about 450 degrees F. as determined by the ring and ball softening point test method specified in AASHTO Designation: M 249-98, section 12.
Concrete is a mixture of paste and aggregates. The paste, composed of Portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction known as hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. Within this process lies the key to a remarkable trait of concrete: it is plastic and malleable when newly mixed, strong and durable when hardened. These qualities explain why concrete, can build superhighways, sidewalks, bridges, warehouse flooring and other traffic media.
All Portland cements are hydraulic cements that set and harden through a chemical reaction with water. During this reaction, called hydration, a node forms on the surface of each cement particle. The node grows and expands until it links up with nodes from other cement particles or adheres to adjacent aggregates.
Curing begins after the exposed surfaces of the concrete have hardened sufficiently to resist marring. Curing ensures the continued hydration of the cement and the strength gain of the concrete. Concrete surfaces are cured by sprinkling with water fog, or by using moisture-retaining fabrics such as burlap or cotton mats. Other curing methods prevent evaporation of the water by sealing the surface with plastic or special sprays (curing compounds).
Some of the deficiencies associated with present pavement marking adhesion include the: (1) inability for signage to be adhered to uncured concrete which, depending on conditions, may take from about 8 days to about 21 days up to six months to exhibit a sufficient bonding surface, (2) inability to be applied due to limited adhesive tack at low temperature; (3) limited ability to accommodate surface roughness; (4) reduced durability, particularly at low temperature, when subjected to impact or shear; (5) increasing adhesion over time which in turn limits the duration of a period during which a temporary installation may be efficiently removed; and (6) staining of light colored concrete roadway surfaces by adhesives in removable markers.
Generally, the application of the thermoplastic or preformed thermoplastic signage requires that the concrete substrate be cured minimally from about 8 days to about 21 days before the application of the thermoplastic or preformed thermoplastic signage with some products requiring up to six months. Most preformed thermoplastic signage require the concrete substrate to be preheated to bring the concrete surface substrate up to a required temperature prior to application of the preformed thermoplastic signage. The signage is then heated over the pre-heated concrete surface to melt the signage into the porous surface of the concrete substrate. It is a feature of the present disclosure that preheating and the thermoplastic heating requirement is avoided.
Where the traffic site is newly constructed concrete, the contracted signage application presently adds days to the completion of the project in that the application of thermoplastic detectable warning devices and pavement markers must have a cured surface to adhere to. In most concrete pedestrian traffic areas the concrete is ready for pedestrian traffic from about 72 hours to about 96 hours whereas the signage requires greater curing time for permanent application thereby leaving the traffic area non-ADA compliant.
Laitance (residual from concrete curing process) on the concrete surface must be removed and cleaned prior to application of the thermoplastic signage. Such residual is cleaned from the concrete surface via grinding or high-pressure washing, leaving the concrete top surface wet. Most signage and adhesives require a clean dry surface for preferred adhesion properties. It is also an additional feature of the present invention that laitance removal is not required to establish a good bond to the Portland cement substrate.
Polyurea coatings may also be comprised of aspartic esters which provide amine functionality and a chemical backbone containing amine linkages. Polyurea is generally used as an industrial coating in severe environments such as with wet or damp surfaces with good chemical resistance to hydrocarbons. Polyurea systems may be applied via spray, 2-part caulk, pour, brush-on or other methods known to those skilled in the art.
In many cases, people tend to mix up polyurea coatings and polyurethane coatings. Thus polyurethane coatings have become a generic term for coating systems based on polyisocyanate reactions. Polyurea coatings normally use amines as coreactants to react with isocyanates. This reaction is extremely fast (within a few seconds or minutes). As a result, polyurea coatings tend to have a very limited pot life and their recoat time becomes a problem in cases where multiple coats are required. A polyurea linkage, however, will have better heat and high temperature resistance than a polyurethane system with polyols as coreactants (post-curing).
Polyurea can be defined as the result of a chemical reaction between an isocyanate and an amine. These amines are generally comprised of polyetheramines and a primary amime chain-extender which is used to impart hardblock content and place the formulation on a volume ratio of about 1:1.
This two-component technology is based on an isocyanate quasi-prepolymer and an amine coreactant. Often an amine resin blend polyurea elastomer is made from an (A) component and a (B) component, where the (A) component has a quasi-prepolymer made from an isocyanate and an active hydrogen-containing material, such as a poly-oxyalkylenepolyamine, as described in U.S. Pat. No. 5,442,034 to Dudley J. Primeaux, II of Huntsman Petrochemical Corporation and herein incorporated by reference. The (B) component includes an amine resin, such as an amine-terminated polyoxyalkylene polyol which may be the same or different from the polyoxyalkylene poly-amine of the quasi-prepolymer. The viscosity of the (A) component is reduced by the inclusion of an organic, alkylene carbonate, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate and the like. The alkylene carbonate also serves as a compatibilizer between the two components, thus provided an improved mix of the system.
Preferably a two-part low viscosity adhesive would comprise a Part (A) component of about 300 centipoise (Cp) and a Part (B) component of about 100 centipoise in an add mixture blend of about 250 centipoise.
U.S. Pat. No. 4,532,274, to Spurr, and assigned to Union Carbide, hereby incorporated by reference, describes epoxied formulations and reactions. An illustration of suitable cycloaliphatic epoxides are as follows:
Formula I
Diepoxides of cycloaliphatic esters of dicarboxylic acids having the formula:
wherein R1 through R9, which can be the same or different are hydrogen or alkyl radicals generally containing one to nine carbon atoms inclusive and preferably containing one to three carbon atoms inclusive as for example methyl, ethyl, n-propyl n-butyl, n-hexyl, 2-ethylhexyl, n-octyl, n-nonyl and the like; R is a valence bond or a divalent hydrocarbon radical generally containing one to nine carbon atoms inclusive and preferably containing four to six carbon atoms inclusive, as for example, alkylene radicals, such as trimethylene, tetramethylene, pentamethylene, hexamethylene, 2-ethylhexamethylene, octamethylene, nonamethylene, and the like; cycloaliphatic radicals, such as 1,4-cyclohexane, 1,3-cyclohexane, 1,2-cyclohexane, and the like.
Particularly desirable epoxides, falling within the scope of Formula I, are those wherein R1 through R9 are hydrogen and R is alkylene containing four to six carbon atoms.
Among specific diepoxides of cycloaliphatic esters of dicarboxylic acids are the following:    bis(3,4-epoxycyclohexylmethyl)oxalate,    bis(3,4-epoxycyclohexylmethyl)adipate,    bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,    bis(3,4-epoxycyclohexylmethyl)pimelate,and the like. Other suitable compounds are described in U.S. Pat. No. 2,750,395 to B. Phillips et al.Formula II
A 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate having the formula:
wherein R1 through R9 which can be the same or different are as defined for R1 in formula I. Particularly desirable compounds are those wherein R1 through R9 are hydrogen.
Among specific compounds falling within the scope of Formula II are the following: 3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-1-methylcyclohexylmethyl, 3,4-epoxy-1-methylcyclohexylmethyl, 3,4-epoxy-1-methylcyclohexanecarboxylate, 6-methyl-3,4-epoxycyclohexylmethyl, 6-methyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-3-methylcyclohexylmethyl, 3,4-epoxy-3-methylcyclohexanecarboxylate, 3,4-epoxy-5-methylcyclochexylmethyl, 3,4-epoxy-5-methylcyclohexanecarboxylate. Other suitable compounds are described in U.S. Pat. No. 2,890,194 to B. Phillips et al.
Formula III
Diepoxides having the formula:
wherein the R single and double primes, which can be the same or different, are monovalent substituents such as hydrogen, halogen, i.e., chlorine, bromine, iodine or fluorine, or monovalent hydrocarbon radicals, or radicals as further defined in U.S. Pat. No. 3,318,822 to Batzer et al. Particularly desirable compounds are those wherein all the R's are hydrogen. Other suitable cycloaliphatic epoxides are the following:
and the like.
The preferred cycloaliphatic epoxides are the following: